ASHRAE REFRIGERATION IP CH 38-2010 FRUIT JUICE CONCENTRATES AND CHILLED JUICE PRODUCTS《浓缩果汁和冷藏果汁产品》.pdf

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1、38.1CHAPTER 38FRUIT JUICE CONCENTRATES AND CHILLED JUICE PRODUCTSORANGE JUICE 38.1Orange Concentrate. 38.1Cold Storage 38.2Concentration Methods 38.3Quality Control 38.4Chilled Juice 38.4Refrigeration 38.5Pure Fruit Juice Powders . 38.5OTHER CITRUS JUICES 38.6NONCITRUS JUICES 38.6Pineapple Juice 38.

2、6Apple Juice . 38.6Grape Juice 38.6Strawberry and Other Berry Juices . 38.7ITRUS products, especially orange juice, comprise the lar-Cgest percentage of the total volume of juices sold in the UnitedStates. Much of the technology used in processing noncitrus juiceswas developed from citrus processing

3、.ORANGE JUICEORANGE CONCENTRATEProcessed orange juice is sold in four principal forms:1. Frozen concentrate (3-plus-1 concentration, in which three vol-umes of water are added to one volume of concentrate for recon-stitution) in a variety of package sizes. These are the familiarretail products.2. Co

4、ncentrate in bulk at 65 Brix. This is an intermediate productthat is bought and sold daily as futures on the CommodityExchange. Most of this product will ultimately be sold in one ofthe other forms.3. Chilled orange juice, which is ready to drink when poured fromthe carton. It is either reconstitute

5、d concentrate or nonconcen-trated juice. By law, these two products must be labeled “fromconcentrate” or “not from concentrate.”4. Institutional or restaurant concentrates in special packaging at4-plus-1 or higher concentrations.After processing, frozen citrus concentrates in retail (3-plus-1)packag

6、es must be stored at 0F. Highly concentrated bulk juice (65Brix) may be satisfactorily stored at about 15F. Chilled single-strength juices are stored at about 30 to 32F.Figure 1 shows a schematic flow diagram of citrus processing.The Brix scale is a hydrometer scale that indicates the percentageby w

7、eight of sugar in a solution at a specified temperature.Selecting, Handling, and Processing Fresh FruitSelection. Fruit is selected for proper quality and maturity.Some fruit that is blemished but sound in quality, referred to aspackinghouse eliminations, is used. A major portion of the crop istaken

8、 directly from the grove to the processing plant. To be mature,the fruit must have the proper Brix-acid ratio and the juice contentand Brix must be above specified values. Fruit should be handledwithout delay because no real maturing occurs after harvesting;instead, the temperature and condition of

9、the fruit determine therate of deterioration. Citrus fruit is sufficiently rugged to withstandmechanical handling on conveyors, elevators, and belts, providedthat the fruit is processed within a day or two after picking. Samplesare taken mechanically as fruit enters the bins, and records ofchemical

10、analyses are maintained. Usually fruit from two or morebins is used simultaneously to improve uniformity. The fruit passesover inspection tables both before and after temporary storage inbins, and damaged or deteriorated fruit is removed.Washing. Before juice extraction, the fruit is wetted by spray

11、s.The wetting agent is dispensed onto the fruit as it travels over rotat-ing brushes. Water sprays near the end of the washer unit rinse thefruit. A sanitizing solution may be used to sanitize conveyors andelevators.Juice Extraction. Individual high-speed mechanical juiceextractors handle from 300 t

12、o 700 pieces of fruit per minute. Somemachines halve the fruit and ream or squeeze the juice from the half.Other machines insert a tube through the middle of the fruit andsqueeze the juice through fine holes into the tube, at the same timesieving away the seeds and large pieces of membrane. After th

13、ejuice has been extracted, it passes to finishers that remove theremaining seeds, pieces of peel, and excess cell or fruit membrane.In the past, this was a comparatively simple process involving one ortwo stages, but it has become complicated in recent years and variesextensively from plant to plant

14、. Usually, one or two stages of screw-type finishers separate most of the pulp from the juice.Pulp washing, in which soluble solids in separated segment andcell walls are recovered by countercurrent extraction with water, ispermitted in Florida, provided that the resultant extract is not used infroz

15、en orange concentrates. It may be used in other formulatedproducts permitted by the Federal Standard of Identity for frozenconcentrated orange juice.The juice or pulp wash liquor from the finishers may requiretreatment in high-speed desludging centrifuges that remove sus-pended matter before transfe

16、rring the juice to the evaporator. Thesecentrifuges have peripheral discharges that open and close at inter-vals to discharge a thick suspension of pulp cells. This operationdecreases the viscosity of juice in the evaporator, improves the effi-ciency of evaporation, and improves the appearance of th

17、e finalproduct. Special means are used to classify orange pulp for inclu-sion in products with a high pulp content.Heat Treatment. When frozen concentrated orange juice wasfirst developed, minimal heat treatment was used to maintain opti-mum flavor. Such concentrate, if prepared from good, sound fru

18、it,remains stable for a considerable time at 0F and for nearly a yearat 5F. However, with large-scale production, it is not possible toensure storage below 5F. Concentrates originally of good qualitytend to gel or clarify rapidly during storage. Heat treatment inacti-vates enzymes responsible for th

19、e development of these defectsduring improper storage. Earlier methods used steam-heated platepasteurizers, but heat treatment is now almost universally includedas an integral part of heat conservation in the evaporation process.The preparation of this chapter is assigned to TC 10.9, Refrigeration A

20、ppli-cation for Foods and Beverages.38.2 2010 ASHRAE HandbookRefrigerationEvaporation-Water Removal. Removal of water follows juiceextraction and preparation. See the section on Concentration Meth-ods for details.Flavor Fortification. Originally, frozen concentrated orangejuice was overconcentrated,

21、 and fresh juice (cutback juice) wasadded to reduce the concentration to the desired level and providefresh flavor in the final product. This process is used extensively infrozen concentrates, but flavor levels cannot be standardized by thismethod alone.Essential oil from orange peel does not by its

22、elf supply com-pletely balanced fresh flavor, but it is now used extensively to con-trol flavor intensity. Some peel oil is found in the cutback juice, butlittle remains in juice from the evaporator. Adding peel oil to the fin-ished concentrate, at approximately 0.014% by volume in the recon-stitute

23、d juice, has become standard practice.Several variations have been introduced to supplement the use ofpeel oil and cutback fresh juice for flavor fortification. In mostcases, vapor from the first stage of concentration is used to producean essence that is restored to the final concentrate to enhance

24、 flavor.Although cutback fresh juice and cold-pressed peel oil are com-monly added, most operations depend heavily on essence recoveryand its incorporation into the final product.Blending, Packaging, and Freezing. The final step in pro-cessing is the blending of concentrate with flavor-enhancing com

25、-ponents such as cold-pressed orange oil and liquid essence. The65 Brix concentrate is then reduced to about 42 Brix, the re-quirement for 3-plus-1 product, which reconstitutes to about 12Brix when used by the consumer. The availability of cold-pressedoil and essence when no fresh fruit is available

26、 makes blendingand packaging possible year-round.Most retail product is packaged in fiber-foil cans, although alu-minum and tinned steel cans may be used. Sizes range from 6 to64 fluid ounces. Gable-top milk cartons and specialized large dis-posable plastic reservoirs for dispensers are also used.Be

27、fore filling, the product is cooled to about 25 to 35F. This isusually done in the swept-surface cold-wall tank in which the concen-trate is blended, but it may also be done in a bladed heat exchanger or,preferably, in a plate-type unit. Alternatively, the 65 Brix concentratefrom the evaporator may

28、be precooled (unblended) and packed in55 gal open-top drums or delivered to large bulk storage tanks.The filled cans pass through blast freezers, where their tempera-ture is reduced to 0F or below in 45 to 90 min. Cans are transportedon link belts, and air handlers are arranged so that air at about

29、25Fis forced down through the loaded belt.Thermal Properties. In calculating cooling and freezing re-quirements, concentrates may be considered to approximate sucrosesolutions of the same concentration. In the range of 60 to 65 Brix,the specific heat is about 0.68 Btu/lbF; for 42 Brix, the value isa

30、bout 0.74 Btu/lbF. Thermal conductivity in the liquid state is inthe range of 0.17 to 0.18 Btuft/hft2F. Regarding the heat offusion for freezing tunnel design, the value should be 70 Btu/lb inthe range of 30 to 0F; however, experience has shown that a valueof about 100 Btu/lb should be used. This al

31、lows for extraneous heatgains, coil defrosting, and so forth.COLD STORAGECold storage facilities for citrus processing can be divided intothree categories according to temperature requirements of 0, 15,and 30F.Fig. 1 Citrus Processing SchematicFig. 1 Citrus Processing SchematicFruit Juice Concentrat

32、es and Chilled Juice Products 38.3Finished goods for retail and institutional markets are stored at0F in insulated, refrigerated buildings. Bulk 65 Brix productpacked in drums is also stored at 0F. The refrigerated buildingsrange from a few thousand square feet to a few acres. Other thanthe usual in

33、sulation requirements, two factors are critical to thedesign: (1) the vapor retarder outside the insulation must be asclose to hermetic as possible, and (2) irrespective of the insulationin the floor, a heat supply must be installed beneath the insulationto maintain the temperature below the floor a

34、t about 32F. Other-wise, the floor will ultimately heave from ice formation below thefloor.The 15F buildings are used for bulk storage of 65 Brix concen-trate. In a typical installation, a 15F building would house severallarge stainless steel tanks, ranging from a few thousand to 200,000 galeach. At

35、 the stated temperature, the product is barely pumpable, re-quiring sanitary positive-displacement pumps. Because the tempera-ture is virtually impossible to change after the product is in the tank,the product must be cooled to storage temperature before it is intro-duced to the tanks. Cooling usual

36、ly occurs in a plate heat exchanger.Finally, 30F storage rooms are used largely for chilled single-strength juice in retail packages or for not-from-concentrate bulktank systems. This product is discussed in the sections on ChilledJuice and Refrigeration.CONCENTRATION METHODSThe three major methods

37、for producing concentrates are (1) high-temperature, single pass, multiple-effect evaporators; (2) freezeconcentration with mechanical separation; and (3) low-temperature,recirculatory, high-vacuum evaporators.Thermally Accelerated Short-Time Evaporator (TASTE)At present, TASTE is the standard evapo

38、rator of the citrus indus-try. This unit has also been successfully applied to grape, apple, andother juices. TASTEs produce at least 90% of all juice concentratein the western hemisphere. The first cost of this unit is among thelowest of all alternatives, and it has excellent thermal efficiency.Fla

39、vor quality and storage stability of juice processed in this unitcompare favorably with those of juice from alternative methods ofconcentration.The TASTE includes all standard methods of heat conservation.It is multiple-effect, uses concurrent vapor for staged preheating,and flashes condensate to di

40、scharge condensed vapors at the lowestpossible temperature. Residence time is minimal because all stagesare single-pass. Total residence time is 2 to 8 min, varying directlywith evaporator capacity.Figure 2 shows a schematic diagram of a typical TASTE. A triple-effect unit illustrates the basic desi

41、gn. Typical units are offered infour to seven effects (five to nine stages), and capacity ranges fromabout 10,000 to 90,000 lb/h water removal. The vapor-to-steamratio is approximately the number of effects times 0.85. In Figure 2,note that juice enters the spray nozzles atop each stage at a temper-

42、ature well above the saturation temperature at which that body oper-ates. The resultant flashing of vapor, combined with the spray effectof the nozzle, distributes the juice on the vertical tube walls. Thus,the juice film and the water vapor flow concurrently down the tube;the juice flows down the w

43、all as the vapor flows in the central areaof the tube. The centrifugal pumps that transfer the juice to the suc-ceeding stage operate continuously in a cavitating, or almost cavi-tating, condition.As juice is transferred from stage 3 to stage 4, it must be reheatedto a higher temperature (140F) to e

44、ffect sufficient flashing. Reheat-ing is typical for any effect that has more than one stage. These stagedivisions are necessary when water removal renders the remainingjuice insufficient to wet the total required surface for that effect.Then flash cooling quickly reduces the concentrate from 117F t

45、othe pump-out temperature of 60F.On a TASTE, vapor flow is fixed and virtually unalterable. Al-though the juice flow shown in Figure 2 is concurrent with the vapor,in many cases it is mixed flow, in which the juice may first be intro-duced to an intermediate effect before being delivered to the firs

46、teffect. In all cases, however, the essence-bearing material must berecovered from the vapor stream that is produced where the juicefirst enters the evaporator.Figure 2 also shows an essence recovery method. Several differ-ent systems for essence recovery are used, some of which are pro-prietary. Th

47、e refrigeration load for essence recovery is relativelysmall, usually 3 to 5 tons, according to evaporator capacity.Freeze ConcentrationIn the freeze concentration system, juice is introduced andpumped rapidly through a swept-surface heat exchanger in whichice nuclei are formed at about 28F. This sl

48、urry is delivered to arecrystallizer, in which small crystals are melted to form larger crys-tals. The slurry of larger crystals, together with the resultant concen-trate, is delivered to the wash column, where the ice rises. As it does,chilled water (melted ice) is introduced at the top to wash the

49、 iceFig. 2 Thermally Accelerated Short-Time Evaporator (TASTE) SchematicFig. 2 Thermally Accelerated Short-Time Evaporator (TASTE) Schematic38.4 2010 ASHRAE HandbookRefrigerationcrystals; these continue to rise and melt as they reach the top of thecolumn. The concentrate (now ice-free) is drawn off the bottom ofthe wash column.At first, centrifuges were used to separate ice crystals from con-centrate, but because of poor separation and attendant problemswith crystal washing, the losses of orange soluble solids were unac-ceptable. The proprietary